This week’s New England Journal of Medicine has 3 articles on brown fat, which have spawned a number of newspaper articles, and this blog. A high concentration of mitochondria color the fat brown, burn huge numbers of calories and produce lots of heat when activated by the cold.

When I was studying physiology in grad school 30 years ago we looked at brown fat as a source of heat for hibernating mammals, and rodents and infants who are unable to shiver to stay warm. We understood it’s role as the maintenance of core temperature.

It's found on infant's backs, but was thought to be minimal or absent from adults. We didn’t know how physiologically active it was in adults. These new studies found brown fat in adults, albeit still in small amounts, in the upper back, the neck, behind the collarbone and along the spine, and showed that it is active, can burn calories and crank heat.

Brown fat is activated by cold. If it can be turned on by medication and burn calories, then it has the potential to be used as a treatment for obesity. It may prove helpful for those with a physiologic cause for obesity, or the magic pill for those who don’t want to eat less and exercise more.

Caution is warranted before jumping on this bandwagon. There are only a small number of humans in these studies, and a bunch of mice. Will activating brown fat cause weight loss, or increase calorie consumption? What other physiologic effects does it have? Fat, once thought as simply a storage cell, is now understood to be a metabolically active tissue.

I’m curious whether those people who never seem to be cold, or tolerate cold with fewer layers than I need have reserves of brown fat. Is brown fat activated by the cold and not yet switched off the source of the sweating when we enter a warm building after a long winter trip? These studies don’t answer this question for us, indeed they could not directly relate the activity of the brown fat in cold with temperature maintenance.

Our fundamental field treatment for hypothermia is to insulate the patient and capture their metabolic heat. Could a medication augment this by turning on brown fat?

All we know sure from these studies is that adults have physiologically active brown fat. The journey to a treatment for obesity, or hypothermia, could be a long one, but if you’re a physiology geek like me, it will be fun.